Method of angle cutting slabs and removing scale

ABSTRACT

An in-line method of producing steel using a continuous caster includes forming a continuous strand of steel from the continuous caster and severing a slab from the continuous strand. An angle between a front face or a rear face of the slab and a line perpendicular to a top surface or a bottom surface of the slab is between about 10° and about 45°. Alternatively, the angle between the front face or the rear face and the line perpendicular to the top surface or the bottom surface is between about 15° and about 35° or between about 20° and about 25°. Primary scale is then removed from the slab with a descaler prior to rolling the slab to a desired thickness. A first waterjet descaler descales only one of the front and the rear faces and only one of the top and bottom surfaces, and a second waterjet descaler descales only the other of the front and the rear faces and only the other of the top and bottom surfaces.

FIELD OF THE INVENTION

[0001] The invention relates generally to the manufacturing of steel articles and, more specifically, to a method of cutting steel slabs at a particular angle to improve the removal of scale using a waterjet process.

BACKGROUND OF THE INVENTION

[0002] One section of a conventional continuous casting line is illustrated in FIG. 1. Initially, molten steel is supplied to a continuous caster 10 that produces a cast steel strand 12. After the strand 12 exits the caster 10, the strand 12 is cut to length with a cutter 16 to produce a series of cast slabs 18 that ride along a rolling table 14. Subsequent to being severed from the strand 12, each slab 18 is transversely fed into a reheat furnace 15 using a transfer machine 20.

[0003] The reheat furnace 15 brings the slab 18 to a uniform temperature to facilitate rolling.

[0004] Upon exiting the reheat furnace 15, the slab 18 is transferred to an upstream end of the rolling table 14. The slab 18 is then descaled in one or more descalers 24, 26, which apply a series of high-pressure waterjets/sprays onto the surface of the slab 18 to remove scale. The slab 18 is then processed by a reversing rolling mill 28 (commonly referred to as a Steckel mill). The rolling mill 28 is typically provided with upstream and downstream coiler furnaces 30, 32. Upon reaching a desired thickness in the rolling mill 28, the intermediate product 34 continues downstream to further processing (not shown). Downstream processing may include shearing the ends of the intermediate product 34, cutting the intermediate product 34 to length and/or coiling the intermediate product 34 into coils.

[0005] A problem associated with this conventional process of forming steel is that the descaler incompletely removes primary scale from the front and rear faces of the slab. Scale, as is well known in the steel industry, begins to form immediately as a slab of steel is cast and is considered an undesirable impurity in the downstream rolling process. Scale is formed by the exposure of the cast steel to air (oxygen), which creates an iron oxide. Scale that forms on the surface of the slab immediately after or during the casting process or during the heating process is known as primary scale, and scale that forms after the primary scale has been removed or during the rolling process is known as secondary scale. Scale that is not removed by descaling becomes part of the intermediate product when the slab is rolled to a desired thickness in the rolling mill. The scale that is introduced into the intermediate product is typically considered a surface defect that can cause a portion of the slab to be undesirably scrapped, reworked, or reclassified as a lower quality product.

[0006] A conventional waterjet descaler 24 is illustrated in FIG. 2. Although a top set of sprayers 40 for the descaler 24 is shown, the descaler 24 can include only a bottom set of sprayers 40 or both a top and bottom set of sprayers 40. As shown, the top set of sprayers 40 are capable of removing scale from the top surface 18 _(T) and partially from the front face 18 _(F) of the slab 18. The second descaler 26 illustrated in FIG. 1 could, for example, be arranged to include a bottom set of sprayers 40 configured to remove scale from the bottom surface 18 _(B) and the rear face 18 _(R) of the slab 18.

[0007] The attack angle α of the sprayers 40 on the waterjet descaler 24 relative to a plane perpendicular to the top 18 _(T) or bottom 18 _(B) surface of the slab 18 is conventionally between 5° and 25° and usually between 10° and 15° with about 15° being typical. This angle β has been optimized to remove scale from the top and bottom surfaces 18 _(T), 18 _(B) of the slab 18. However, by optimizing the angle α for the top and bottom surfaces 18 _(T), 18 _(B), the angle α is not optimized to remove scale from the front and rear 18 _(F), 18 _(R) faces of the slab 18. Thus, when a single set of sprayers 40, which are oriented to optimally remove scale from one surface (i.e., the top surface 18 _(T)), are used to remove scale from a non-optimized additional surface (i.e., the front 18 _(F) face), scale is incompletely removed from the additional surface.

[0008] Although additional descalers can be added to the casting line that have sprayers oriented for optimally removing scale from the front and rear faces of the slab, the costs associated with adding these additional descalers is prohibitive. Furthermore, many preexisting rolling lines have limited space for adding such additional equipment to the line, and the installation of additional equipment to the line may not be possible due to space limitations. Thus, there is a need to adapt preexisting equipment and/or processes to improve the efficiency of removing scale from slabs.

SUMMARY OF THE INVENTION

[0009] This and other needs are met by the present invention, which in accord with one aspect includes forming a continuous strand of steel from a continuous caster and severing a slab from the continuous strand. The slab is severed such that an angle between a front face or a rear face of the slab and a line perpendicular to a top surface or a bottom surface of the slab is between about 10° and about 45°. Alternatively, the angle between the front face or the rear face and the line perpendicular to the top surface or the bottom surface is between about 15° and about 35° or between about 20° and about 25°. Primary scale is then removed from the slab with a waterjet descaler prior to rolling the slab to a desired thickness. By adjusting the angle of the faces of the slab relative to the top and bottom of the slab, the faces are more optimally presented towards the descaler. Thus, more scale can be removed from the front and rear faces of the slab, which reduces contamination of the intermediate product from unremoved scale during the rolling process.

[0010] In another aspect of the invention, the angle at which the slab is severed is defined by the angle between the front face or rear face of the slab and a line defined by water sprays of the descaler. This angle can be between about 30° and about 70°. Alternatively, the angle can be between about 30° and about 50° or between about 35° and about 40°.

[0011] In still another aspect of the invention, a single descaler descales only one of the front and the rear faces and only one of the top and bottom surfaces. A second descaler is used to descale only the other of the front and rear faces and only the other of the top and bottom surfaces. As such, one descaler only descales two surfaces of the slab, and the other descaler only descales the other two surfaces of the slab.

[0012] Additional advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein only an exemplary embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein:

[0014]FIG. 1 is a schematic perspective of a section of a conventional continuous casting, reheating, descaling and rolling line;

[0015]FIG. 2 is a schematic side view of a slab being descaled by a conventional descaler;

[0016]FIG. 3 is a schematic side view of a slab being severed from a strand according to an embodiment of the present invention;

[0017]FIGS. 4A and 4B are schematic sides views illustrating different placements of sprayers of a descaler relative to one another; and

[0018]FIG. 5 is a schematic side view of a slab severed in accordance to an embodiment of the present invention being descaled by a descaler.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention improves removal of scale from a slab during a waterjet descaling process by angle cutting the slab from a strand. By angle cutting the slab, the front and rear faces are presented to the sprayers of the waterjet descaler at an angle that promotes improved access to the front and rear faces by the sprayers. As the sprayers have better attack or impingement angles to the front and rear faces of the slab, the removal of scale from the front and rear faces of the slab is improved in comparison to scale removal of a conventionally severed slab.

[0020] The conventional method of severing the slab from the strand results in front and rear faces (see FIG. 2) that are perpendicular (90°) with respect to a top or bottom surface of the slab. In contrast, the slab is severed at a non-right angle relative to a top or bottom surface of the slab in one aspect of the current invention. The method of severing the slab is not limited as to a particular process or apparatus used to sever the slab. Example methods of severing a slab include water jet, plasma cut, mechanical/saw cut, and sheer cut. In a current aspect, however, the slab is severed with an oxy-fuel torch.

[0021] As illustrated in FIG. 3, the angle θ at which the slab 18 is severed from the strand is defined between a line perpendicular to one of a top surface 18 _(T) or bottom surface 18 _(B) of the slab 18 and one of a front face 18 _(F) or rear face 18 _(R) of the slab 18. In one aspect of the invention, the angle θ is defined between the front face 18 _(F) and the top surface 18 _(T) of the slab 18. In so doing, the forward-leading point 18 _(P) of the slab 18 is located at the bottom leading portion of the slab 18, which facilitates rolling of the slab 18 in certain subsequent processes. The invention, however, is not limited in this manner, as the forward-leading point 18 _(P) can be located on the top of the slab 18. The slab 18 can then be turned over prior to reheating or rolling to reorient the forward-leading point 18 _(P) to the bottom of the slab 18.

[0022] In one aspect of the invention, the angle θ is between about 10° and about 45°. As will be discussed in more detail below, by changing the angle θ from the conventional 0°, a descaler used in a subsequent descaling process has a better attack angle to the front and rear faces 18 _(F), 18 _(R) of the slab 18.

[0023] In an another aspect of the invention, the angle θ is between about 15° and about 35°. By reducing the range of the angle θ to between about 15° and about 35°, the slab 18 can be more easily severed. For example, at a greater angle θ , such as 45°, the cutter is required to cut through a greater thickness of the slab 18. Additionally, feeding the slab 18 into a rolling mill becomes difficult as the angle θ approaches 45°. In still another aspect of the invention, the angle θ is between about 20° and about 25°. It has been determined that this range provides an optimal tradeoff between ease of cutting and facilitating the efficiency of the subsequent descaling process.

[0024] As used herein, the angle θ is defined between a first line perpendicular to a straight line defined by the top surface 18 _(T) or bottom surface 18 _(B) of the slab 18 and a second line defined by the front face 18 _(F) or rear face 18 _(R) of the slab 18. As the top and bottom surfaces 18 _(T), 18 _(B) and the front and rear faces 18 _(F), 18 _(R) of the slab 18 are unlikely to be perfectly straight, the positions of the lines can be obtained using a linear regression of three or more evenly-spaced positions on the top surface 18 _(T) or bottom surface 18 _(B) and the front face 18 _(F) or rear face 18 _(R) of the slab 18.

[0025] Upon being severed from the strand, the slab 18 can undergo any number of conventional processing steps prior to descaling and rolling. For example, the slab 18 can be introduced into a reheat furnace, which is used to stabilize the temperature of the slab 18, such that the temperature throughout the slab is substantially even prior to rolling.

[0026] Also, as explained previously, the slab is subject to a descaling process to remove scale formed on the slab prior to rolling. In certain aspects, the scale removed by the descaler is primary scale. However, the invention is not limited in this manner, as the scale removed from the slab can be secondary scale. Also, the descaler can be a waterjet descaler. As is known in the art, a waterjet descaler 24 can have top and bottom sets of sprayers 40 that are opposite one another, as illustrated in FIG. 4A, or have the top and bottom sets of sprayers 40 separated, as illustrated in FIG. 4B. Alternatively, the top and bottom sprayers 40 of the descaler 24 can be separated in different booths (not shown).

[0027] The process parameters of the descaler are not limited to particular ranges. However, referring to FIG. 5, the attack angle α of the sprayers 40 on the waterjet descaler 24 relative to a plane perpendicular to the top surface 18 _(T) or bottom surface 18 _(B) of the slab 18 can be between about 5° and about 25°. Also, in certain aspects, the attack angle α can between about 10° and about 15° and is typically set to about 15°. The spray volume of the descaler 24 can be between about 12 and about 30 gallons per minute per inch of slab width. However, in certain other aspects, the spray volume can be between about 21 and about 26 gallons per minute per inch of slab width. The pressure of the fluid in the descaler 24 can be between about 1600 and about 3200 psi, and in certain other aspects, the pressure can be between about 2500 and about 2800 psi.

[0028] In an alternative aspect of the invention, the angle θ at which the slab is severed from the strand can be defined, in part, by the attack angle α of the sprayers 40 of the waterjet descaler 24. As used herein, the attack angle ac of the sprayers 40 is defined between a line perpendicular to the top 18 _(T) or bottom surface 18 _(B) of the slab 18 and a straight line defined by the average direction of the sprayers 40 of the waterjet descaler 24. However, each sprayer 40 of the waterjet descaler 24 may be aligned slightly differently from one another. In such a situation, the directional orientation of each sprayer 40 can be averaged over the entirety of the waterjet descaler 24, assuming that each sprayer 40 emits substantially similar water flow, to obtain the straight line defining the average direction of the sprayers 40. The directional orientation of each sprayer 40 can be obtained from the directional orientation of a sprayer orifice 42 in each sprayer 40 from which the water is directed onto the slab 18.

[0029] The angle β of the sprayers 40 relative to the front face 18 _(F) or rear face 18 _(R) of the slab 18 is the angle θ at which the slab 18 is severed plus the attack angle α of the sprayers 40. In one aspect of the invention, the angle β is between about 30° and about 70°. In an another aspect of the invention, the angle β of the sprayers 40 is between about 30° and about 50°. By reducing the range of the angle β, the slab can be more easily severed. In still another aspect of the invention, the angle β of the sprayers 40 is between about 35° and about 40°. It has been determined that this further reduced range for the angle β provides an optimal tradeoff between ease of cutting of the slab 18 and facilitating the descaling of the front and rear faces 18 _(F), 18 _(R) of the slab 18.

[0030] The present invention can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention can be practiced without resorting to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention.

[0031] Only an exemplary aspect of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. 

What is claimed is:
 1. An in-line method of producing steel using a continuous caster, comprising the steps of: forming a continuous strand of steel from the continuous caster; and severing a slab from the continuous strand, wherein an angle between a front or a rear face of the slab and a line perpendicular to a top or a bottom surface of the slab is between about 10° and about 45°.
 2. The in-line method of producing steel according to claim 1, wherein the angle between the front or the rear face and the line perpendicular to the top or the bottom surface is between about 15° and about 35°.
 3. The in-line method of producing steel according to claim 1, wherein the angle between the front or the rear face and the line perpendicular to the top or the bottom surface is between about 20° and about 25°.
 4. The in-line method of producing steel according to claim 1, further comprising removing scale from the slab with a descaler.
 5. The in-line method of producing steel according to claim 4, further comprising rolling the slab to a desired thickness.
 6. The in-line method of producing steel according to claim 5, wherein primary scale is removed by the descaler prior to rolling the slab to the desired thickness.
 7. The in-line method of producing steel according to claim 4, wherein the descaler is a water sprayer, and water entering the sprayer is at a pressure between about 1600 and about 3200 and at a flow rate between about 12 and about 30 gallons per minute per inch of slab width.
 8. The in-line method of producing steel according to claim 4, wherein the descaler is a water sprayer, and water entering the sprayer is at a pressure between about 2500 and about 2800 and at a flow rate between about 21 and about 26 gallons per minute per inch of slab width.
 9. The in-line method of producing steel according to claim 4, wherein the descaler descales only one of the front and the rear faces and only one of the top and bottom surfaces.
 10. The in-line method of producing steel according to claim 9, further comprising a second descaler, wherein the second descaler descales only the other of the front and the rear faces and only the other of the top and bottom surfaces.
 11. The in-line method of producing steel according to claim 1, wherein the angle is between the front face and the bottom surface.
 12. An in-line method of producing steel using a continuous caster, comprising the steps of: forming a continuous strand of steel from the continuous caster; and severing a slab from the continuous strand; and removing scale from the slab with a descaler, the descaler including water jets positioned at an attack angle relative to a top or a bottom surface of the slab, wherein an angle of the water sprayers relative to a front or a rear face of the slab is between about 30° and about 70°.
 13. The in-line method of producing steel according to claim 12, wherein the attack angle of the water sprayers relative to the front or the rear face is between about 30° and about 50°.
 14. The in-line method of producing steel according to claim 12, wherein the attack angle of the water sprayers relative to the front or the rear face is between about 35° and about 40°.
 15. The in-line method of producing steel according to claim 12, further comprising rolling the slab to a desired thickness.
 16. The in-line method of producing steel according to claim 15, wherein primary scale is removed by the descaler prior to rolling the slab to the desired thickness.
 17. The in-line method of producing steel according to claim 12, wherein water entering the sprayer is at a pressure between about 1600 and about 3200 and at a flow rate between about 12 and about 30 gallons per minute per inch of slab width.
 18. The in-line method of producing steel according to claim 12, wherein water entering the sprayer is at a pressure between about 2500 and about 2800 and at a flow rate between about 21 and about 26 gallons per minute per inch of slab width.
 19. The in-line method of producing steel according to claim 12, wherein the descaler descales only one of the front and the rear faces and only one of the top and bottom surfaces.
 20. The in-line method of producing steel according to claim 19, further comprising a second descaler, wherein the second descaler descales only the other of the front and the rear faces and only the other of the top and bottom surfaces. 